Idaho County free press. [volume] (Grangeville, Idaho Territory) 1886-current, 1887-12-23
TESTING A GREAT LENS.
VISIT TO THE WORKSHOP OF THE
LATE ALVAN CLARK.

Finishing the Object Glass of q Great
MISUNDERSTANDING with the Palm of
the Hand-A Peep at Star-A
Story.
In 1882 / called to see Alvan Clark, the
distinguished constructor of telescopes. who
has just died ] found him at his home IN
Cambridgeport, Mass. His sons were busy
putin. the finishing touches to the great
telescope object glass then being made for
the Russian Astronomical observatory at
Pulkova. The Pulkova objective was to he
! placed in a temporary mounting that very
evening to be tested for the first time on
celestial objects.
1t is i'll the after correction and perfecting
of the objective which calls for the special
skill which has made Alvau ClarkS name so
famous. The large objectives, such as the
| Pulkova and Lick glasses, are ground and
polished by machinery. Two levers work in
opposite directions, aud are so arranged that
any part of tie glass surface may be reached,
doing the work. The final polish which is of
the most delicate nature imaginable, is done
with the surface of the hand. Mr.. Clark went
so far as to say that one revolution of tue
hand i'll excess would change the correction.
On a table was the finished Pulkova lens,
which weighed $50 pounds, and consiste of
Generally these lenses are made to accurately
fit and are joined together with Canada bal
sam, but i'll such large glasses as the Pulkova
and the Lick, they are fitted in a metal frame
with an adjustment SO that they can be made
to approach each other, or otherwise.
When the evening was sufficiently advanced
the great Pulkova glass was placed in its tenn
porary fitting in the garden There was no
moon and the darkness was intense. The glass
was brought out on a four wheel hand truck
and lifted into the tube by five men and fixed
10y revolving it in the screw fitting. The tube
was forty-fve feet long and weighed with he
attending fittings about seven tons Two piles
| of brickwork supported the whole There
was no clockwork movement and the rough
est apparatus was employed, the telescope was
raised and moved Ivy a guide rope, the mo-
ton of an equatorial movement being imi-
tated 10y using Il common wndlass. As the
motion of the earth caused the object to pass
across the field of the telescope, the observer
gave the order "follow," when a slight turn
of the wndlass kept the object in view. Such
were the rough appliances used to test this
$50, 100 lens.
VIEW OF FIXED STAR
The planets had all set, and had to be sat
istied with view of a fixed star, which is an
excellent object for testing the optical proper
ties of lens but very embarrassing other
wise, rs the arg, st telescope can make little
impression on a fixed star; disk can be
seen, merely speck of light The star Sc
lected a small one and barely visible as
n pale, minute object. On looking at it with
this magnificent instrument it's wonderful
light gathering powers were at once evident,
for the star shone with the luster and brill
fancy of an electric light. 1t was an object
ngII mt o11 In
the glass and to the eyes of Mr. Clark and
his sons many were evident, and, it was said,
two months work was necessary to correct
them During the trial the lens were lowered
md five men revolved the glass in its fitting
On its being placed III position again one of
! the sons was about to make another test when
the old man shouted: Wait boys, let her
| cooln
l curious to know what this could
mean, and Alva Clark explained that the cor
lection was SO delicate that the leat from the
hands of the five holding the metal case
of the objective would change the correction,
so it had to ''cool."
III conversation with Mr. Clark on the
advantages of immense telescopes such as this
one, he admitted that the telescopes of mod
crate aperture, say from ten to fifteen
inches, were preferable for general use even
for the highest purposes. He spoke with
pride of such an instrument he had made,
wiGh which he had seen all that could be seen
even with colossal telescopes. Only one dis
covery has been made with the Washington
telescope of twenty-six inches diameter during
its many years of use. The Russian Pulkova
instrument, delivered by the Clarks in 1882,
has never been heard from, and those who
expect immediate and extraordinary results
from the Lick thirty-six inch objective will
probably be disappointed. These huge tele-
scopes are great light gatherers and useful
for Photographic and spectroscopic work but
their definitions of the surface of the moon
aud the planets are Disappointing
A story is told of French astronomer who
Travelled hundreds of miles to look through
the great Ross telescope. When asked what
he would like to see lie called for the planet
Saturn, which was then i'll good position On
looking through the telescope and finding the
wretchecl definition of the object he said:
"You tell me | have looked at the planet
Saturn, SO | must believe have done so; but
| was not aware of the fact john Michels
in New York Sun
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